Backport: feat(mcp): expose statusCode, url, responseBody on MCPClientError#15610
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…5605) ## Summary Adds `statusCode`, `url`, and `responseBody` to `MCPClientError` so downstream consumers can branch on HTTP context structurally instead of regex-parsing the error message. All three fields are optional and unset for stdio transport / non-response failures (network errors, aborts), so this is fully backward compatible. Populated at the four HTTP throw sites in `mcp-http-transport.ts`: - POST `!response.ok` → `statusCode`, `url`, `responseBody` - POST `text/event-stream` missing body → `statusCode`, `url` - POST unexpected content-type → `statusCode`, `url` - GET SSE failure → `statusCode`, `url` ## Why The MCP spec requires clients using streamable HTTP transport to fall back to legacy SSE transport when the server returns `404` (or `405`) on the streamable HTTP endpoint. To implement that correctly, the caller needs the response status — but today `MCPClientError` only exposes the message string. ## Validation - `pnpm --filter @ai-sdk/mcp type-check` ✓ - `pnpm --filter @ai-sdk/mcp test:node` — 208 passed ✓ - `pnpm --filter @ai-sdk/mcp test:edge` — 208 passed ✓ - `pnpm --filter @ai-sdk/mcp build` ✓ - Added integration tests asserting `statusCode` / `url` / `responseBody` for 404 (POST, with the "does not support HTTP transport" message), 500 (POST, with body), and 503 (GET SSE failure).
aayush-kapoor
approved these changes
May 27, 2026
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This is an automated backport of #15605 to the release-v6.0 branch. FYI @allenzhou101